Submitted to: Plant Physiology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/10/2006
Publication Date: 5/14/2007
Citation: Narayanan, N.N., Vasconcelos, M.W., Grusak, M.A. 2007. Expression profiling of Oryza sativa metal homeostasis genes in different rice cultivars using a cDNA macroarray. Plant Physiology and Biochemistry. 45(5):277-286. Interpretive Summary: Rice is an important food crop, but it is a poor source of essential micronutrients such as iron and zinc. Because human micronutrient deficiencies are common in regions of the world that are dependent on rice, we are interested in improving the iron and zinc concentration of rice grains through plant breeding or biotechnology. To achieve this, we need more information on the genes and mechanisms within plants that help to move iron and zinc from leaves to developing seeds. In this study, we developed a special membrane that allows us to simultaneously measure the levels of 36 genes in rice. The genes chosen were ones that encode for proteins that are involved in the movement or storage of zinc or iron. We studied these levels in leaves of four diverse rice cultivars, which show differing concentrations of iron or zinc in their seeds. Of the 36 genes studied, our membrane identified 12 genes that were active in rice leaves of all four cultivars. Additional molecular techniques identified another nine genes that also were active. These results are helping us to determine which genes are important in the distribution of iron and zinc within the plant. This information will help us develop more nutritious rice cultivars.
Technical Abstract: Rice is an important food crop, but it is a poor source of essential micronutrients such as iron and zinc. In order to improve the metal ion content of rice grains through breeding or biotechnology, more information is needed on the molecular players that help mobilize metals from leaves to developing seeds. To profile several genes simultaneously, a cDNA macroarray was developed using 36 metal-related genes from rice, including ZIPs, NRAMPs, and YSLs (coding for known or potential metal transporters), as well as NAS, FER, FRO, NAAT, FDH, GSTU, and PDR (involved in metal homeostasis). Because flag leaves are the major source of phloem-delivered photoassimilates and remobilized metals for developing seeds, we analyzed the expression of these metal-related genes in flag and non-flag leaves of four different rice cultivars (Cocodrie, Taipei 309, IR58, and IR68144) during the period of mid-grain fill. Twenty-four of 36 genes exhibited low to non-detectable signals in the macroarray, while 12 genes (OsIRT1, OsZIP1, OsZIP5, OsZIP8, OsYSL5, OsYSL6, OsYSL7, OsYSL8, OsYSL18, OsNRAMP2, OsNRAMP4, and OsNRAMP7) were found to be highly expressed in both flag and non-flag leaves of all four cultivars. Additional expression analysis using semi-quantitative or quantitative PCR provided results that were generally consistent with the macroarray, but semi-quantitative PCR confirmed that OsFDH, OsFER1, OsNAAT, OsNAS1, OsPDR9, OsYSL12, OsYSL13, OsZIP7, and OsZIP10 were also expressed in leaves. This specialized macroarray has provided a short list of potential candidate genes, expressed in leaves, which might contribute to the process of metal transport to distant sinks, such as seeds.